Recessing RMG metal gate stack for forming self-aligned contact

ABSTRACT

Embodiments of the present invention may include methods of incorporating an embedded etch barrier layer into the replacement metal gate layer of field effect transistors (FETs) having replacement metal gates, as well as the structure formed thereby. The embedded etch stop layer may be composed of embedded dopant atoms and may be formed using ion implantation. The embedded etch stop layer may make the removal of replacement metal gate layers easier and more controllable, providing horizontal surfaces and determined depths to serve as the base for gate cap formation. The gate cap may insulate the gate from adjacent self-aligned electrical contacts.

BACKGROUND

The present invention relates to semiconductor devices, and particularlyto recessing the gate dielectric and work function metals of areplacement metal gate field effect transistor (FET).

FETs are commonly employed in electronic circuit applications. FETs mayinclude a source region and a drain region spaced apart by asemiconductor channel region. In planar FETs, the semiconductor channelregion may be a semiconductor substrate. In finFETs, the semiconductorchannel region may be a semiconductor fin. A gate, potentially includinga gate dielectric layer, a work function metal layer, and a metalelectrode, may be formed next to the channel region. By applying voltageto the gate, the conductivity of the channel region may increase andallow current to flow from the source region to the drain region.

Due in part to the relative instability of the dielectric layer and workfunction metal layer of the gate, a gate-last process, or replacementmetal gate process, may be used where a sacrificial gate is formed priorto forming other components of the FET. The sacrificial gate may then beremoved to form a recessed region that may then be filled with areplacement metal gate potentially including a gate dielectric layer, awork function metal layer, and a metal electrode. Because thereplacement metal gate is formed after the other components of the FET,it is not subjected to various potentially damaging processing steps,for example high-temperature anneals. Prior to forming the metalelectrode, the gate dielectric layer and the work function metal layermay be recessed to a height less than the height of the recessed regionto reduce the gate resistance.

SUMMARY

According to an embodiment, a method is disclosed. The method mayinclude: forming a first embedded etch stop layer in a gate dielectriclayer and a work-function metal layer of a replacement metal gate (RMG)using ion implantation. The first embedded etch stop layer may becomposed of a layer of dopant atoms embedded at a depth below an upperportion of the gate dielectric layer and an upper portion of thework-function metal layer.

According to another embodiment, a method is disclosed. The method mayinclude: removing a dummy gate from a field effect transistor (FET)structure to form a gate recess region, the FET structure comprising thedummy gate formed on a substrate, a spacer adjacent to the dummy gate,and a source-drain region adjacent to the spacer; forming a gatedielectric layer in the gate recess region, the gate dielectric layerhaving an upper surface that is substantially flush with an uppersurface of the spacer; forming a work-function metal layer on the gatedielectric layer, the work-function metal layer having an upper surfacethat is substantially flush with an upper surface of the spacer; forminga first embedded etch stop layer in the gate dielectric layer and thework-function metal layer using ion implantation, wherein the firstembedded etch stop layer may be composed of a layer of dopant atomsembedded at a depth below an upper portion of the gate dielectric layerand an upper portion of the work-function metal layer; removing theupper portion of the gate dielectric layer; removing the upper portionof the work-function metal layer; removing the first embedded etch stoplayer to expose a lower portion of the gate dielectric layer and a lowerportion of the work-function metal layer; forming a gate electrode onthe lower portion of the gate dielectric layer and the lower portion ofthe work-function metal layer; and forming a gate cap in the gate recessregion, the gate cap having an upper surface that is substantially flushwith an upper surface of the spacer and an upper surface of aninterlevel dielectric (ILD) layer adjacent to the spacer.

According to another embodiment, a structure is disclosed. The structuremay include: a gate dielectric layer on a substrate; a work-functionmetal layer on the gate dielectric layer, the work-function metal layerhaving an upper surface that is substantially flush with an uppersurface of the gate dielectric layer; a gate electrode on the uppersurface of the gate dielectric layer and the upper surface of thework-function metal layer; a gate cap above the gate electrode, the gatecap having an upper surface that is substantially flush with an uppersurface of a spacer that is adjacent to the gate cap, the gateelectrode, and the gate dielectric layer; and a first embedded etch stoplayer in the spacer, the first embedded etch stop layer adjacent to thegate dielectric and comprising dopant atoms. The structure may alsoinclude a second embedded etch stop layer between the gate electrode andthe gate cap, the second embedded etch stop layer extending laterallyinto the spacer and comprising dopant atoms.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a cross section view depicting a field effect transistor (FET)structure having a dummy gate, according to an embodiment of the presentinvention.

FIG. 2 is a cross section view depicting removing the dummy gate of theFET to form a gate recess region, according to an embodiment of thepresent invention.

FIG. 3 is a cross section view depicting depositing a gate dielectriclayer and work function metals in the gate recess region, according toan embodiment of the present invention.

FIG. 4 is a cross section view depicting forming a first embedded etchstop layer in the gate dielectric and work function metals, according toan embodiment of the present invention.

FIG. 5 is a cross section view depicting removing portions of the gatedielectric layer and work function metals above the first embedded etchstop layer, according to an embodiment of the present invention.

FIG. 6 is a cross section view depicting removing the first embeddedetch stop layer, according to an embodiment of the present invention.

FIG. 7 is a cross section view depicting forming a gate electrode abovethe remaining portions of the gate dielectric layer and the workfunction metals, according to an embodiment of the present invention.

FIG. 8 is a cross section view depicting forming a second embedded etchstop layer in the gate electrode, according to an embodiment of thepresent invention.

FIG. 9 is a cross section view depicting removing the portion of thegate electrode above the second embedded etch stop layer, according toan embodiment of the present invention.

FIG. 10 is a cross section view depicting forming a gate cap above thesecond embedded etch stop layer, according to an embodiment of thepresent invention.

FIG. 11 is a cross section view depicting forming self-aligned contacts,according to an embodiment of the present invention.

FIG. 12 is a cross section view depicting removing a portion of thesecond embedded etch stop layer, according to an embodiment of thepresent invention.

FIG. 13 is a cross section view depicting forming a gate cap on the gateelectrode, according to an embodiment of the present invention.

FIG. 14 is a cross section view depicting forming self-aligned contacts,according to an embodiment of the present invention.

Elements of the figures are not necessarily to scale and are notintended to portray specific parameters of the invention. For clarityand ease of illustration, dimensions of elements may be exaggerated. Thedetailed description should be consulted for accurate dimensions. Thedrawings are intended to depict only typical embodiments of theinvention, and therefore should not be considered as limiting the scopeof the invention. In the drawings, like numbering represents likeelements.

DETAILED DESCRIPTION

Detailed embodiments of the claimed structures and methods are disclosedherein; however, it can be understood that the disclosed embodiments aremerely illustrative of the claimed structures and methods that may beembodied in various forms. This invention may, however, be embodied inmany different forms and should not be construed as limited to theexemplary embodiments set forth herein. Rather, these exemplaryembodiments are provided so that this disclosure will be thorough andcomplete and will fully convey the scope of this invention to thoseskilled in the art.

For purposes of the description hereinafter, the terms “upper”, “lower”,“right”, “left”, “vertical”, “horizontal”, “top”, “bottom”, andderivatives thereof shall relate to the disclosed structures andmethods, as oriented in the drawing figures. It will be understood thatwhen an element such as a layer, region, or substrate is referred to asbeing “on”, “over”, “beneath”, “below”, or “under” another element, itmay be present on or below the other element or intervening elements mayalso be present. In contrast, when an element is referred to as being“directly on”, “directly over”, “directly beneath”, “directly below”, or“directly contacting” another element, there may be no interveningelements present. Furthermore, the terminology used herein is for thepurpose of describing particular embodiments only and is not intended tobe limiting of the invention. As used herein, the singular forms “a,”“an,” and “the” are intended to include the plural forms as well, unlessthe context clearly indicates otherwise.

In the interest of not obscuring the presentation of embodiments of thepresent invention, in the following detailed description, someprocessing steps or operations that are known in the art may have beencombined together for presentation and for illustration purposes and insome instances may have not been described in detail. In otherinstances, some processing steps or operations that are known in the artmay not be described at all. It should be understood that the followingdescription is rather focused on the distinctive features or elements ofvarious embodiments of the present invention.

Embodiments of the present invention may include methods ofincorporating an embedded etch barrier layer into the replacement metalgate layer of field effect transistors (FETs) having replacement metalgates, as well as the structure formed thereby. Because the typicalprocess of fabricating FETs having replacement metal gates involvesmultiple etching and planarizing steps, the gate height of FET may varydue to the cumulative variation of each etching and planarizing step,which may ultimately lead to reduced device performance, increaseddevice variability, or inoperability. By incorporating an embedded etchbarrier layer into the replacement metal gate layer, embodiments of thepresent invention may, among other potential benefits, reduce gateheight variation by planarizing the replacement metal gates to aconsistent level (i.e., the level of the embedded etch barrier).

Referring to FIG. 1 a field effect transistor (FET) structure 100 may beprovided or fabricated. The FET structure 100 may include a sacrificialgate 120 above a substrate 110. A pair of source-drain regions 140 maybe adjacent to substrate 110 on opposite sides of the sacrificial gate120, separated from the sacrificial gate 120 by spacers 130. Thesubstrate 110 may be covered by an interlevel dielectric (ILD) layer 150having a top surface that is substantially flush with the top surface ofthe sacrificial gate 120.

In the depicted embodiment, FET structure 100 is a planar device so thatthe substrate 110 may be a bulk semiconductor substrate. In suchembodiments, the substrate 110 may be made from any of several knownsemiconductor materials such as, for example, silicon, germanium,silicon-germanium alloy, carbon-doped silicon, carbon-dopedsilicon-germanium alloy, and compound (e.g. III-V and II-VI)semiconductor materials. Non-limiting examples of compound semiconductormaterials include gallium arsenide, indium arsenide, and indiumphosphide. In an embodiment, the substrate 110 may be approximately, butis not limited to, several hundred microns thick. For example, thesubstrate 110 may have a thickness ranging from approximately 0.5 mm toapproximately 1.5 mm. In other embodiments where the FET structure is aplanar device, the substrate 110 may be a semiconductor-on-insulator(SOI) substrate, where a buried insulator layer separates a basesubstrate from a top semiconductor layer. The components of the FETstructure 100 may then be formed in or adjacent to the top semiconductorlayer.

In another embodiment, the FET structure 100 may be a fin field effecttransistor (“finFET”), in which case the substrate 110 may be asemiconductor fin. While embodiments depicted in FIGS. 1-11 refer to aplanar device, a person of ordinary skill in the art will understandthat the method described will apply equally to finFET devices. In yetanother embodiment, the FET structure 100 may be a nanowire field effecttransistor, in which case the substrate 110 may be a semiconductornanowire or a stack of nanowires. While embodiments depicted in FIGS.1-11 refer to a planar device, a person of ordinary skill in the artwill understand that the method described will apply equally to nanowiredevices.

The sacrificial gate 120 may have a height ranging from approximately 30nm to approximately 200 nm, preferably approximately 50 nm toapproximately 100 nm. Because the replacement metal gate that will laterreplace the sacrificial gate 120 may be planarized to height less thanits initial height (FIG. 11), the sacrificial gate 120 may have a heightgreater than the ultimately desired height of the replacement metalgate. The sacrificial gate 120 may include any of a sacrificialdielectric layer, a sacrificial gate electrode, and a hard mask layerabove the sacrificial gate electrode (not shown). The sacrificialdielectric layer may be made of any known dielectric material such assilicon oxide or silicon nitride. The sacrificial gate electrode may bemade of, for example, an amorphous or polycrystalline silicon material.Other suitable materials for the sacrificial dielectric layer and thesacrificial gate electrode known in the art may also be used. Thesacrificial dielectric layer and the sacrificial gate electrode may beformed by any suitable deposition technique known in the art, includingatomic layer deposition (ALD), chemical vapor deposition (CVD), physicalvapor deposition (PVD), molecular beam deposition (MBD), pulsed laserdeposition (PLD), or liquid source misted chemical deposition (LSMCD).

The hard mask may be formed above the sacrificial gate electrode toprotect the sacrificial gate electrode during subsequent fabricationprocesses. The hard mask may be made of an insulating material, such as,for example, silicon nitride, silicon oxide, silicon oxynitrides, or acombination thereof, may have a thickness ranging from approximately 20nm to approximately 50 nm, and may be formed by any suitable depositiontechnique known in the art, including ALD, CVD, PVD, MBD, PLD, or LSMCD.

The spacers 130 may be formed on the sidewalls of the sacrificial gate120. The spacers 130 may be made of any insulating material, such assilicon nitride, silicon oxide, silicon oxynitrides, or a combinationthereof. In some embodiment, the spacers 130 may be made of so-called“low-k” dielectric material with a relative dielectric constant lessthan 7. Exemplary low-k materials are SiBCN and SiOCN. The spacers 130may have a thickness ranging from 2 nm to approximately 100 nm,preferably approximately 2 nm to approximately 25 nm. In someembodiments, the spacers 130 may be made of the same material as thehard mask described above. In some embodiments, the spacers 130 may bemade of a material different from the hard mask. In a preferredembodiment, the hard mask and the spacers 130 may be made of siliconnitride. The spacers 130 may be formed by any method known in the art,including depositing a conformal silicon nitride layer over thesacrificial gate 120 and removing unwanted material from the conformalsilicon nitride layer using a anisotropic etching process such as, forexample, reactive ion etching (RIE) or plasma etching (not shown).Methods of forming spacers are well-known in the art and other methodsare explicitly contemplated. Further, in various embodiments, thespacers 130 may include one or more layers. While the spacers 130 areherein described in the plural, the spacers 130 may consist of a singlespacer surrounding the sacrificial gate 120.

The source-drain regions 140 may be formed on the substrate 110 adjacentto the spacers 130. Numerous methods of forming source-drain regions areknown in the art, any of which may be used to form the source-drainregions 140. In some embodiments, the source-drain regions 140 may beformed by doping portions of the substrate 110 (not shown). In otherembodiments, including the embodiment depicted in FIG. 1, thesource-drain regions 140 may be formed by growing epitaxialsemiconductor regions adjacent to the substrate 110. The epitaxialsemiconductor regions may extend above and/or below the top surface ofthe substrate 110 as shown.

The ILD layer 150 may be deposited on the substrate 110, thesource-drain regions 140, the spacers 130, and the sacrificial gate 120.The ILD layer 150 may be composed of any suitable dielectric material,for example, silicon oxide, silicon nitride, hydrogenated silicon carbonoxide, silicon based low-k dielectrics, flowable oxides, porousdielectrics, or organic dielectrics including porous organic dielectricsand may be formed using any suitable deposition techniques includingALD, CVD, plasma enhanced CVD, spin on deposition, or PVD. In someembodiments, various barriers or liners (not shown) may be formed belowthe ILD layer 150. After depositing the ILD layer 150, the ILD layer 150may be planarized, using for example chemical-mechanical planarization(CMP), so that the sacrificial gate 120 is exposed and a top surface ofthe ILD layer 150 is substantially flush with the top surface of thesacrificial gate 120.

Referring to FIG. 2, the sacrificial gate 120 may be removed to form agate recess region 210 above the substrate 110 and between the spacers130. The sacrificial gate 120 may be removed by any suitable etchingprocess known in the art capable of selectively removing the sacrificialgate 120 without substantially removing material of the substrate 110,the spacers 130, or the ILD layer 150. In an exemplary embodiment, thesacrificial gate 120 may be removed, for example, by a reactive ionetching (RIE) or plasma etching process, in conjunction with wet etchingprocessing.

Referring to FIG. 3, a gate dielectric layer 311 and one or more workfunction metals, including for example, work-function metals 313 a-313 cmay deposited in the gate recess region 210. While the embodimentdepicted in FIG. 3 includes 3 work function metal layers, otherembodiments may include more or less layers. In some embodiments, thegate dielectric layer 311 and the work-function metals 313 a-313 c mayfill the gate recess region 210.

The gate dielectric layer 311 may be made of, for example, siliconoxide, hafnium oxide, zirconium oxide, aluminum oxide, titanium oxide,lanthanum oxide, strontium titanium oxide, lanthanum aluminum oxide, ormixtures thereof. Other suitable gate dielectric materials may be knownin the art. The physical thickness of the gate dielectric layer 311 mayvary, but typically may have a thickness ranging from approximately 0.5nm to approximately 10 nm.

The work-function metals 313 a-313 c may be made of, for example,aluminum, lanthanum oxide, magnesium oxide, strontium titanate, tantalumcarbide, titanium nitride, and strontium oxide. In an exemplaryembodiment, work function metals 313 a and 313 c may be made of the samematerial, for example, titanium nitride, while the work function metal313 b sandwiched between them may be made of a different material, forexample tantalum carbide. The work-function metals 313 a-313 c maythickness ranging from approximately 0.5 nm to approximately 5 nm,though greater and lesser thickness are explicitly contemplated. Thethickness of the topmost work function metal 313 c may have a thicknesssufficient to fill the gate recess region 210.

The gate dielectric layer 311 and the work-function metals 313 a-313 cmay be formed by any suitable deposition technique, such as, but notlimited to, atomic layer deposition (ALD), chemical vapor deposition(CVD), physical vapor deposition (PVD), molecular beam deposition (MBD),pulsed laser deposition (PLD), or liquid source misted chemicaldeposition (LSMCD), sputtering, or plating. In some embodiments, aplanarization process, such as CMP, may be performed after thedeposition of the gate dielectric layer 311 and the work-function metals313 a-313 c to remove so that an upper surface of the gate dielectriclayer 311 and an upper surface of the work-function metals 313 a-313 cmay be substantially flush with the upper surface of the ILD layer 150.

Referring to FIG. 4, a first embedded etch stop layer 410 may be formedin the work function metals 313 a-313 c. The first embedded etch stoplayer 410 may be formed by implanting barrier dopants into the workfunction metals 313 a-313 c. In some embodiments, including theembodiment depicted in FIG. 4, the first embedded etch stop layer 410may also be formed in the gate dielectric layer 311, the spacers 130,and the ILD layer 150 as well during the implantation process.

Suitable barrier dopants for use in the first embedded etch stop layer410 may include, for example, any atom or ion capable of beingcontrollably implanted into the work function metals 313 a-313 c and thegate dielectric layer 311 at a desired depth, and subsequently remainunaffected by etching of the work function metals 313 a-313 c and gatedielectric layer 311 above the first embedded etch stop layer 410.Exemplary barrier dopants may include silicon, carbon, and nitrogenimplanted by ion implantation. In one embodiment, the barrier dopantsmay include nitrogen implanted with an energy ranging from 5 KeV to 100KeV and a dose ranging from 10¹⁵ atoms×cm⁻² to 10¹⁶ atoms×cm⁻². Thefirst embedded etch stop layer 410 may have a thickness ranging fromapproximately 3 nm to approximately 10 nm and may be formed at a depthof approximately 10 nm to approximately 40 nm, measured from the uppersurface of the work function metals 313 a-313 c. While the firstembedded etch stop layer 410 is depicted in FIG. 4 as a uniform layer,the first embedded etch stop layer 410 may include any number ofdifferent regions, with each region made of a combination of the barrierdopant and a material of one of the work function metals 313 a-313 c,the gate dielectric layer 311, the spacers 130, and the ILD layer 150.

Referring to FIG. 5, portions of the work function metals 313 a-313 cand the gate dielectric layer 311 above the first embedded etch stoplayer 410 may be removed to form a first gate recess 510. The first gaterecess 510 may have a bottom that is defined by an upper surface of thefirst embedded etch stop layer 410. The portions of the work functionmetals 313 a-313 c and the gate dielectric layer 311 above the firstembedded etch stop layer 410 may be removed using any suitable etchingprocess capable of selectively removing the material of the workfunction metals 313 a-313 c and the gate dielectric layer 311 withoutsubstantially removing the material of the first embedded etch stoplayer 410. In an exemplary embodiment, the portions of the work functionmetals 313 a-313 c above the first embedded etch stop layer 410 may beremoved by an aqueous etchant containing ammonium hydroxide and hydrogenperoxide. Optionally, the gate dielectric layer 311 above the firstembedded etch stop layer 410 may be removed by an aqueous etchantcontaining hydrofluoric acid.

Referring to FIG. 6, the first embedded etch stop layer 410 (FIG. 5) maybe removed to expose the remaining portions of the work function metals313 a-313 c and the gate dielectric layer 311, and form a deep gaterecess 610. The deep gate recess 610 may have a bottom that is definedby an upper surface of the remaining portions of the work functionmetals 313 a-313 c and the gate dielectric layer 311. The first embeddedetch stop layer 410 may be removed using any suitable etching processcapable of selectively removing the material of the first embedded etchstop layer 410 without substantially removing the material of the workfunction metals 313 a-313 c, the gate dielectric layer 311, the spacers130, and the ILD layer 150. In an exemplary embodiment, the firstembedded etch stop layer 410 may be removed by a dry etch process suchas reactive ion etch (RIE).

Referring to FIG. 7, a gate electrode 710 may be formed in the deep gaterecess 610 (FIG. 6). The gate electrode may be made of any suitable gateconductor material such as, but not limited to, zirconium, tungsten,tantalum, hafnium, titanium, aluminum, ruthenium, metal carbides, metalnitrides, transition metal aluminides, tantalum carbide, titaniumcarbide, tantalum magnesium carbide, or combinations thereof. The gateelectrode 710 may be formed by any suitable deposition process, such as,but not limited to, ALD, CVD, PVD, MBD, PLD, LSMCD, sputtering, orplating. If after deposition the gate electrode 710 overfills the firstgate recess 510, the gate electrode 710 may be planarized, for exampleby chemical-mechanical planarization (CMP), so that an upper surface ofthe gate electrode 710 is substantially flush with the upper surface ofthe ILD layer 150.

Referring to FIG. 8, a second embedded etch stop layer 810 may be formedin the gate electrode 710. The second embedded etch stop layer 810 maybe formed by implanting barrier dopants into the gate electrode 710. Insome embodiments, including the embodiment depicted in FIG. 4, the firstembedded etch stop layer 410 may also be formed in the gate dielectriclayer 311, the spacers 130, and the ILD layer 150 as well during theimplantation process.

Suitable barrier dopants may include, for example, any atom or ioncapable of being controllably implanted into the gate electrode 710 at adesired depth, and subsequently remain unaffected by etching of the gateelectrode 710 above the second embedded etch stop layer 810. Exemplarybarrier dopants may include silicon, carbon, and nitrogen implanted byion implantation. In one embodiment, the barrier dopants may includenitrogen implanted with an energy ranging from 5 KeV to 60 KeV and adose ranging from 10¹⁵ atoms×cm⁻² to 10¹⁶ atoms×cm⁻². The secondembedded etch stop layer 810 may have a thickness ranging fromapproximately 3 nm to approximately 8 nm and may be formed at a depth ofapproximately 10 nm to approximately 50 nm, measured from the uppersurface of the gate electrode 710. While the second embedded etch stoplayer 810 is depicted in FIG. 8 as a uniform layer, the second embeddedetch stop layer 810 may include any number of different regions, witheach region made of a combination of the barrier dopant and a materialof one of the gate electrode 710, the spacers 130, and the ILD layer150.

Referring to FIG. 9, a portion of the gate electrode 710 above thesecond embedded etch stop layer 810 may be removed to form a second gaterecess 850. The second gate recess 850 may have a bottom that is definedby an upper surface of the second embedded etch stop layer 810. Theportion of the gate electrode 710 above the second embedded etch stoplayer 810 may be removed using any suitable etching process capable ofselectively removing the material of the gate electrode 710 withoutsubstantially removing the material of the second embedded etch stoplayer 810. In an exemplary embodiment, the portion of the gate electrode710 above the second embedded etch stop layer 810 may be removed by anaqueous etchant containing hydrogen peroxide.

Referring to FIG. 10, a gate cap 910 may be formed in the second gaterecess 850. The gate cap 910 may be composed of insulating material,such as a nitride, an oxide, or an oxynitride. In an embodiment, thegate cap 910 and the second embedded etch stop layer 810 may serve as abi-layer gate cap. The gate cap 910 may be formed by any suitabledeposition process, such as, but not limited to, ALD, CVD, PVD, MBD,PLD, LSMCD, sputtering, or plating. If after deposition the gate cap 910overfills the second gate recess 850, the gate cap 910 may beplanarized, for example by chemical-mechanical planarization (CMP), sothat an upper surface of the gate cap 910 is substantially flush withthe upper surface of the ILD layer 150.

Referring to FIG. 11, an upper dielectric layer 1102 and contacts 1104may be formed on the structure 100. The upper dielectric layer 1102 maybe formed on the upper surface of the ILD layer 150, the spacers 130,and the gate cap 910. The upper dielectric layer 1102 may besubstantially similar to the ILD layer 150 and may formed usingsubstantially similar techniques as those describe above with referenceto FIG. 1.

The contacts 1104 may be formed removing portions of the upperdielectric layer 1102, the ILD layer 150, and portions of the secondembedded etch stop layer 810 and the first embedded etch stop layer 410that are composed of the barrier dopants and the ILD layer 150 selectiveto the gate cap 910, the spacers 130, and the source-drain regions 140to form contact openings (not shown). The contact openings may expose anupper surface of the source drain regions 140. In an embodiment, thecontact openings may be formed using a conventional etching process,such as, for example, RIE. The contact openings may then be filled witha conductive material to form the contacts 1104. In an embodiment, theconductive material may be a metal or metal alloy composed of, forexample, Cu or Al. A bottom surface of the contacts 1104 may be incontact with the upper surface of the source-drain regions 140. Becauseof the selective nature of the etching process used to form the contactopenings, the contacts 1104 may be referred to as self-aligned contacts.As shown in FIG. 11, the gate cap 910 and the second embedded etch stoplayer 810 may insulate the gate electrode 710, the gate dielectric layer311, and the work-function metals 313 a-313 c from the contacts 1102.

Another embodiment by which to recess the gate dielectric and workfunction metals of a replacement metal gate is described in detail belowby referring to the accompanying drawings FIGS. 12-14. In the presentembodiment, the second embedded etch stop layer 810 may be removed afterthe second gate recess 850 is formed as described above with referenceto FIG. 9. Accordingly, FIG. 12 can be considered a continuation of theprocess after FIG. 9.

Referring to FIG. 12, the second embedded etch stop layer 810 may beremoved after the second gate recess 850 is formed (FIG. 9) to form adeep gate cap recess 1202. The second embedded etch stop layer 810 maybe removed using any suitable etching process capable of selectivelyremoving the material of the second embedded etch stop layer 810 withoutsubstantially removing the material of the gate electrode 710, thespacers 130, and the ILD layer 150. In an exemplary embodiment, thefirst embedded etch stop layer 410 may be removed by a dry etchingprocess such as RIE. In such an embodiment, the gate cap 910 may beformed directly on the gate electrode 710.

Referring to FIG. 13, a gate cap 1302 may be formed in the deep gate caprecess 1202 (FIG. 12). The gate cap 1302 may be composed of insulatingmaterial, such as a nitride, an oxide, or an oxynitride. The gate cap1302 may be formed by any suitable deposition process, such as, but notlimited to, ALD, CVD, PVD, MBD, PLD, LSMCD, sputtering, or plating. Ifafter deposition the gate cap 1302 overfills the deep gate gap recess1202, the gate cap 1302 may be planarized, for example bychemical-mechanical planarization (CMP), so that an upper surface of thegate cap 1302 is substantially flush with the upper surface of the ILDlayer 150.

Referring to FIG. 14, an upper dielectric layer 1402 and contacts 1404may be formed on the structure 100. The upper dielectric layer 1402 maybe formed on the upper surface of the ILD layer 150, the spacers 130,and the gate cap 910. The upper dielectric layer 1402 may besubstantially similar to the ILD layer 150 and may formed usingsubstantially similar techniques as those describe above with referenceto FIG. 1.

The contacts 1404 may be formed removing portions of the upperdielectric layer 1402, the ILD layer 150, and portions of the secondembedded etch stop layer 810 and the first embedded etch stop layer 410that are composed of the barrier dopants and the ILD layer 150 selectiveto the gate cap 1302, the spacers 130, and the source-drain regions 140to form contact openings (not shown). The contact openings may expose anupper surface of the source drain regions 140. In an embodiment, thecontact openings may be formed using a conventional etching process,such as, for example, RIE. The contact openings may then be filled witha conductive material to form the contacts 1404. In an embodiment, theconductive material may be a metal or metal alloy composed of, forexample, Cu or Al. A bottom surface of the contacts 1404 may be incontact with the upper surface of the source-drain regions 140. Becauseof the selective nature of the etching process used to form the contactopenings, the contacts 1404 may be referred to as self-aligned contacts.As shown in FIG. 14, the gate cap 1302 may insulate the gate electrode710, the gate dielectric layer 311, and the work-function metals 313a-313 c from the contacts 1402.

Embodiments of the present invention may provide a new approach forprecisely controlling the metal gate recess depth during reverse metalgate (RMG) fabrication by forming an embedded etch layer in the metalgate stack and then etching the top portion of the metal gate stackselectively to the embedded etch stop layer. This technique may improvethe removal of workfunction metals in gates, typically composed ofdifferent metals sandwiched together, because the embedded etch stoplayer may provide a flat and uniform surface for etching the differentmetals. This may aide in the formation of a gate recess, at acontrollable depth, in which a dielectric capping layer may be formed toisolate the gate from a subsequent source-drain contact.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiment, the practical application or technicalimprovement over technologies found in the marketplace, or to enableother of ordinary skill in the art to understand the embodimentsdisclosed herein. It is therefore intended that the present inventionnot be limited to the exact forms and details described and illustratedbut fall within the scope of the appended claims.

What is claimed is:
 1. A structure comprising: a gate dielectric layeron a substrate; a work-function metal layer on the gate dielectriclayer, the work-function metal layer having an upper surface that issubstantially flush with an upper surface of the gate dielectric layer;a gate electrode on the upper surface of the gate dielectric layer andthe upper surface of the work-function metal layer; a gate cap above thegate electrode, the gate cap having an upper surface that issubstantially flush with an upper surface of a spacer that is adjacentto the gate cap, the gate electrode, and the gate dielectric layer; anda first embedded etch stop layer embedded in the spacer, the firstembedded etch stop comprising dopant atoms.
 2. The structure of claim 1,further comprising: a second embedded etch stop layer between the gateelectrode and the gate cap, the second embedded etch stop layerextending laterally into the spacer and comprising dopant atoms.
 3. Thestructure of claim 1, further comprising: an interlevel dielectric (ILD)layer on the substrate adjacent to the spacer, the ILD layer having anupper surface that is substantially flush with an upper surface of thegate cap; an upper dielectric layer formed on the gate cap, the spacer,and the ILD layer; an electrical contact extending through the upperdielectric layer and the ILD layer, wherein the electrical contact is incontact with the gate cap, the spacer, and an upper surface of asource-drain region that is adjacent to the spacer.
 4. The structure ofclaim 1, wherein the first embedded etch stop layer is located between atop insulating material layer and a bottom insulator material layer thatcomprise the spacer.
 5. The structure of claim 1, wherein the dopantatom of the first embedded etch stop layer comprises silicon, carbon, ornitrogen.
 6. The structure of claim 1, wherein an inner sidewall of thefirst embedded etch stop layer contacts an outer sidewall of the gateelectrode.
 7. The structure of claim 1, wherein a topmost surface of thefirst embedded etch stop layer is coplanar with a topmost surface of thegate electrode.
 8. The structure of claim 1, wherein the work-functionmetal layer comprises a stack of a first work-function metal layer, asecond work-function metal layer and a third work-function metal layer.9. The structure of claim 8, wherein the first work-function metal layerand the and the second work-function metal layer are both U-shaped, andhave a topmost surface that is coplanar with a topmost surface of thegate dielectric layer.
 10. The structure of claim 1, wherein the gateelectrode has outermost sidewalls that are vertical aligned withoutermost sidewalls of the gate dielectric layer.
 11. The structure ofclaim 1, wherein a second embedded etch stop layer comprising a dopantatom is located above the first embedded etch stop layer and is entirelyembedded in the spacer.
 12. The structure of claim 11, wherein thesecond embedded etch stop layer has an inner sidewall that contacts thegate cap.
 13. The structure of claim 11, wherein the second embeddedetch stop layer is located between a top insulating material layer ofthe spacer and a bottom insulator material layer of the spacer.
 14. Thestructure of claim 11, wherein the dopant atom of the second embeddedetch stop layer comprises silicon, carbon, or nitrogen.
 15. Thestructure of claim 11, wherein the second embedded etch stop layer has abottommost surface that is coplanar with a bottommost surface of thegate gap.